1. Field of the Invention
The present invention relates to an optical information recording apparatus for recording a data pulse signal on an optical recording medium.
2. Description of the Related Art
An optical information recording apparatus for writing a data pulse signal consisting of consecutive pairs of mark (indicia) and space on an optical information recording medium such as CD (compact disk) and DVD (digital video disk or digital versatile disk) is known.
In such optical information recording apparatus, a drive power (more specifically, drive current) for a semiconductor laser is on-off controlled in short periods in response to a write command signal to intermittently irradiate a laser beam at short periods, and this laser beam is used as a write beam to be irradiated onto the information recording medium via an optical system.
When, further, information is written on a high density information recording medium such as information writable DVD-R (write once DVD) or DVD-RW (rewritable DVD), for example, control called write pulse strategy is performed to write and form pits having suitable recording characteristics on a recording layer.
FIGS. 1A and 1B of the accompanying drawings illustrate a write pulse strategy employed for DVD-R when information is written on a recording layer made from an organic pigment, and FIGS. 2A and 2B illustrate a write pulse strategy for DVD-RW when information is written on a recording film made from a phase change material.
As shown in FIGS. 1A and 1B, the DVD-R write pulse strategy provides a drive current to be fed to a semiconductor laser corresponding to recordation data in the form of pulse train and produces a write beam corresponding to recordation mark lengths of the recordation data according to a top pulse and subsequent multi-pulses, rather than simply conducting on-off control the drive current to be fed to the semiconductor laser in accordance with amplitude variations of the recordation data.
If the drive current for the semiconductor laser is controlled under such DVD-R write pulse strategy, thermal interference among the organic pigments of the recording layer is suppressed, and it is possible to prevent a rear end of a resulting pit from bulging and becoming like a tear drop due to heat accumulation. This also results in prevention of occurrence of jitter and crosstalk so that the DVD-R write pulse strategy is effective measures to improve recording characteristics.
If the thermal interference occurs, a jitter component tends to appear at the edge of the recordation mark, and if the rear end of the pit bulges and becomes like a teardrop, crosstalk to a neighboring track increases. DVD-R write pulse strategy prevents the thermal interference from occurring and the pit rear end from becoming like a tear drop so that it can prevent the jitter and crosstalk.
In the DVD-RW write pulse strategy, as shown in FIGS. 2A and 2B, a drive current to the semiconductor laser corresponding to the recordation data is given in the form of pulse train, and a write beam corresponding to recordation mark lengths of the recordation data is generated in response to the top pulse, multi-pulses and cool pulse.
If the drive current of the semiconductor laser is controlled on the basis of this DVD-RW write pulse strategy, the laser beam power varies between recordation power and bias power in accordance with the top and multi-pulses, and this variation causes the phase change material of the recording layer to be melt and cooled repeatedly such that amorphous is formed. Further, a laser beam of erasure power is irradiated during periods corresponding to the spaces of the recordation data so that the phase change material is crystallized. In this manner, the drive current of the semiconductor laser is controlled with the top, multi- and cool pulses to form recordation pits thereby improving recordation characteristics.
Conventionally, the characteristics of recordation on the high density information recording medium are improved by controlling the recordation power of the write beam with the above described write pulse strategy or the like. However, since the semiconductor laser element has an individual difference and environmental changes influence the semiconductor laser characteristics, it is sometimes difficult to set the recordation power of the write beam at a suitable power.
When, for example, information is written onto the same information recording media with different pickups, waveforms (time width and intensity) of laser beams emitted from respective semiconductor laser elements are different from each other and it is difficult to have similar recording characteristics on the information recording media even if the semiconductor lasers are driven and controlled on the basis of the same strategy pattern. Specifically, the laser beam emitted from one semiconductor laser according to the common strategy pattern has such a waveform as shown in FIG. 3A, and the laser beam emitted from the other semiconductor laser according to the commom strategy pattern has such a waveform as shown in FIG. 3B. These waveforms are different from each other in rise time, fall time and irradiation period Ta and Tb so that the recordation characteristics on the information recording media are not the same as each other.
When, further, information is written on the same information recording media with the same pickup, characteristics of an optical control circuit, which is an electric circuit, and operation characteristics of the semiconductor laser change because they are influenced by environmental temperature and other factors. This makes it difficult to have uniform recording characteristics on the information recording media which is similar to the case where there are differences between the respective laser elements. Specifically, as shown in FIG. 4A, when a drive current to a semiconductor laser is controlled on the basis of a write pulse, a propagation delay period of the optical control circuit (a period until an in-phase output and inverted output are generated in response to a write pulse; see also FIGS. 4B and 4C) generally varies with the environmental temperature, and a rise time tPLH and a fall time tPHL of the propagation delay period also vary. If, for example, the rise time tPLH increases and the fall time tPHL decreases, the time for the drive current to drive the semiconductor laser becomes shorter and the irradiation time for the laser beam becomes shorter than an intended time period.
Moreover, the environmental temperature may influence not only the semiconductor laser element and optical control circuit, but also other circuits and electronic parts such as power source circuit used to drive the semiconductor laser element and optical control circuit. This results in non-uniform characteristics of the laser beams emitted from the semiconductor lasers and makes it difficult to have the same recordation characteristics on the information recording media.